The present invention relates to a high-frequency weldable thermoplastic rubber composition, to a method of rendering non-polar thermoplastic rubbers high-frequency weldable, to a high-frequency weldable shaped article obtainable from the composition according to the invention, to a method for manufacturing said shaped articles and to a method of high-frequency welding of said articles. Furthermore, the present invention relates to shaped high-frequency welded articles obtainable by the method according to the present invention.
Shaped articles of conventional thermoplastic rubber compositions comprising a thermoplastic polyolefin homopolymer or copolymer and an olefinic rubber which is fully crosslinked, partially crosslinked or not crosslinked and/or block-copolymer of styrene/conjugated diene/styrene and/or its hydrogenated derivative, optionally in the presence of common additives can only be adhered together by using adhesives or they must be heat welded by the hot air or hot plate method. Conventional adhesion methods are disadvantageous in terms of the need to modify the adhering surface, (for instance, by priming, corona treatment, etching, etc.), selecting the suitable adhesive, etc. Additionally, the hot air and hot plate method can only be carried out at a relatively slow speed. Furthermore, the temperature resulting in an acceptable welding without burning or scorching the surface is difficult to be controlled.
In many sheeting applications the sheets are formed, cut to shape and assembled to make the final part, such as, for example chemical protective suits, inflatable boats, inflatable containers and roofing articles. In the assembly of sheet materials, a preferred method is high-frequency welding due to speed and complexity of the shape to be welded. High-frequency welding is, however, not feasible with those thermoplastic elastomers due to their lack in polarity. However, there is a need in the industry to render those thermoplastic elastomers weldable by the high-frequency welding method.
U.S. Pat. No. 4,728,566 pertains to a composite article comprising a polymer foam having HF-bonded thereto at least one surface layer, wherein the HF-bonding is effected by a layer of HF-bondable polymer film between said foam and said surface layer, said HF-bondable polymer film comprising a carbon monoxide-containing olefin interpolymer and said polymer foam being selected from the group consisting of various foamed polymers. The surface layer is selected from the group comprising polymers, fabrics, leather, cellulosic products, wood, vitreous materials, metal foils, paper and foams and the HF-bondable polymer film comprises at least one of copolymer of ethylene and carbon monoxide (ECO), copolymer of ethylene, carbon monoxide and acrylic acid (ECOAA), copolymer of ethylene, carbon monoxide and methacrylic acid (ECOMAA) and copolymer of ethylene, carbon monoxide and vinyl acetate (ECOVA).
U.S. Pat. No. 2,667,437 discloses a method to heat-weld two non-polar, unmodified thermoplastics by exposing them to a pair of hot electrodes which are covered with a fixed conductive polymer.
U.S. Pat. No. 4,268,388 pertains to almost the same welding-method as disclosed in U.S. Pat. No. 2,667,437.
U.S. Pat. No. 3,336,173 discloses the addition of a polyamide to non-polar thermoplastics in order to obtain a HF-weldable product without taking into consideration the very poor properties of such a blend due to the lack of compatibility between the non-polar thermoplastic and the polar polyamide.
EP-A-0,028,106 discloses the use of a special bituminous petroleum derivative as a HF-welding promoter in chlorinated PE/chlorosulfonated PE.
U.S. Pat. No. 6,326,084 describes a method of high-frequency welding of non-polar thermoplastic elastomers characterized in that said elastomers comprise a polar modifier selected from functionalized polyolefins or functionalized block-copolymers of styrene/conjugated diene/styrene.
U.S. Pat. No. 4,273,894 discloses thermoplastic compositions for the manufacture of transparent, weldable and flexible articles which composition essentially consists of 60 to 95% by weight of at least one chlorinated polyolefin and 5 to 40% by weight of at least one copolymer of butadiene, styrene and an acrylic acid or a metacrylic acid ester.
It is an object of the present invention to render non-polar thermoplastic rubbers which are weldable by high-frequency welding techniques while maintaining good elastic properties such as Shore A in the range of about 20 to about 95, preferably about 35 to about 90.
It is a further object to provide a method for welding of thermoplastic elastomers without impairing its elastic properties.
It is a third object of the present invention to provide shaped articles having improved properties.
These and further objects become evident from the description of the invention.
In a first embodiment the present invention relates to a modified thermoplastic rubber composition comprising
(A) a thermoplastic rubber comprising
(i) a rubber; and
(ii) a thermoplastic polyolefin homopolymer or copolymer; and
(B) a polar modifier in an amount effective to render said thermoplastic rubber composition high-frequency weldable, wherein the polar modifier is selected from the group consisting of
(a) thermoplastic polyurethane resins, in an amount of at least about 25 wt.-%, based on the total amount of thermoplastic rubber (A) and thermoplastic polyurethane resin (a);
(b) chlorinated polyolefin resins;
(c) copolymers of ethylene and vinyl acetate;
(d) terpolymers of styrene, butadiene and acrylonitrile; and
(e) mixtures thereof.
In a second embodiment the present invention relates to a method of rendering a thermoplastic rubber (A) comprising
(i) a rubber; and
(ii) a thermoplastic polyolefin homopolymer or copolymer;
high-frequency weldable by addition of an effective amount of a polar modifier (B) selected from the group consisting of
(a) thermoplastic polyurethane resins, in an amount of at least 25 wt.-%, based on the total amount of thermoplastic rubber (A) and thermoplastic polyurethane resin (a);
(b) chlorinated polyolefin resins;
(c) copolymers of ethylene and vinyl acetate;
(d) terpolymers of styrene, butadiene and acrylonitrile; and
(e) mixtures thereof.
In a third embodiment the present invention relates to a high-frequency (HF) weldable shaped article comprising in a blend a thermoplastic rubber (A) comprising
(i) a rubber; and
(ii) a thermoplastic polyolefin homopolymer or copolymer; and
an effective amount of a polar modifier (B) selected from the group consisting of
(a) thermoplastic polyurethane resins, in an amount of at least 25 wt.-%, based on the total amount of thermoplastic rubber (A) and thermoplastic polyurethane resin (a);
(b) chlorinated polyolefin resins;
(c) copolymers of ethylene and vinyl acetate;
(d) terpolymers of styrene, butadiene and acrylonitrile; and
(e) mixtures thereof.
In a fourth embodiment the present invention relates to a method for manufacturing a high-frequency (HF) weldable shaped article comprising the steps of
blending
(A) a thermoplastic rubber comprising
(i) a rubber; and
(ii) a thermoplastic polyolefin homopolymer or copolymer;
with an effective amount of
(B) a polar modifier selected from the group consisting of
(a) thermoplastic polyurethane resins, in an amount of at least 25 wt.-%, based on the total amount of thermoplastic rubber (A) and thermoplastic polyurethane resin (a);
(b) chlorinated polyolefin resins;
(c) copolymers of ethylene and vinyl acetate;
(d) terpolymers of styrene, butadiene and acrylonitrile; and
(e) mixtures thereof
and
forming the resulting thermoplastic rubber composition into the shaped article.
In a fifth embodiment the present invention relates to a method of bonding surfaces of the shaped articles as defined above comprising the steps of contacting the respective surfaces of said shaped articles to be welded together and subjecting said surfaces to high-frequency (HF) welding conditions.
In a sixth embodiment the present invention relates to a shaped welded article obtainable by the HF-welding method described above.
Alternative or preferred embodiments of the present invention become apparent from the dependent claims and the description which follows.
The thermoplastic elastomer compositions according to the present invention facilitate the manufacturing of welded articles of non-polar thermoplastic rubbers having complex shapes which welded articles have high mechanical stability, high tear resistance and weld-strength within the weld of up to about 20, preferably about 25, more preferably about 30 N/cm.